Method of manufacturing lamellar composites

ABSTRACT

A METHOD OF MANUFACTURING LAMELLAR COMPOSITES BY MEANS OF DIRECTIONALLY DEMIXING SOLID MATERIALS HAVING A EUTECTOID COMPOSITION, OR SOLID SOLUTIONS. THE STARTING MATERIALS MUST HAVE A GRAIN SIZE OF MORE THAN APPROXIMATELY 0.1 MM. THE MATERIALS ARE DIRECTIONALLY DEMIXED WHILE USING A TEMPERATURE GRADIENT OF AT LEAST 10*C. PER CM. WHICH IS PASSED THROUGH THE BODY AT A RATE WHICH IS LEE THAN OR EQUAL TO THE MAXIMUM DEMIXING RATE.

United States Patent 3,694,193 METHOD OF MANUFACTURING LAMELLARCOMPOSITES Franciscus Marinus Anna Carpay and Adrianus Martinus JacobusGerardus van Run, both of Emrnasingel, Eindhoven, Netherlands NoDrawing. Filed Oct. 6, 1970, Ser. No. 78,575 Claims priority,application Netherlands, Aug. 15, 1970, 7012088 Int. Cl. C22c 33/00, N02

US. Cl. 75-129 2 Claims ABSTRACT OF THE DISCLOSURE A method ofmanufacturing lamellar composites by means of directionally demixingsolid materials having a eutectoid composition, or solid solutions. Thestarting materials must have a grain size of more than approximately 0.1mm. The materials are directionally demixed while using a temperaturegradient of at least C. per cm. which is passed through the body at arate which is less than or equal to the maximum demixing rate.

The invention relates to a method of manufacturing bodies of lamellarcomposites by directionally demixing solid single-phase materials whichdemix discontinuously in two or more phases upon cooling. Thesesingle-phase materials may have a eutectoid composition or may consistof solid solutions. Lamellar composites are understood to mean materialswhose grains consist of at least two phases in which at least one of thephases in at least one direction has a dimension which is relativelymuch larger than the dimensions in the other directions. These materialsthus comprise both composites whose grains are built up from thin sheetsof alternatively the one and the other phase and composites one phase ofwhich consists of needles which are embedded in a different phase.

Discontinuous demixing, sometimes also referred to as cellular demixing,is understood to mean that the new phases are produced by nucleation andgrowth from the grain boundaries at which the composition of thetransformed matrix remains uniform except for the incoherent boundary ofthe growing cell. Methods of directionally coagulating melts of mixturesof materials are known (see, for example, US. Pat. 3,124,452). Generallymethods are used which are also employed in the manufacture ofmonocrystalline materials in which the molten material is allowed tocool off in a previously determined direction such as, for example, inthe method according to Bridgman. If in this manner mixtures ofmaterials are treated which upon coagulation from the melt constitute atleast two phases of lamellar geometry, then it is found afterwards thatthe lamellae in the coagulated material in all grains have grownsubstantially perpendicularly onto the coagulation front. However, intheir transverse cross-section the lamellae different grains aregenerally not in parallel. In A Study of Directionally TransformedPearlite by B. L. Bramfitt and A. R. Marder, IMS Proceedings (1968)pages 43-55, the use of directional cool ing is described for aniron-carbon alloy having a eutectoid composition. However, pearliteobtained from austenite in this method does not have the structure as isobtained when directionally coagulating mixtures of materials. Thelamellae in the grains are substantially not parallel to thetransformation direction. An object of the present invention is toprovide a method of manufacturing bodies of lamellar composites bydirectionally demixing solid singlephase materials which demixdiscontinuously in two or more phases upon cooling in such a manner thatthe lamellae in all grains are substantially parallel to the trans-3,694,193 Patented Sept. 26, 1972 formation direction. It was found thatthis condition can be satisfied by a method which is characterized inthat a single-phase material is directionally demixed whose grains havea diameter of not less than approximately 0.1 mm. while using atemperature gradient of at least 10 C. per cm. passed through the bodyat a rate which is less than or equal to the maximum rate of demixing.It was found that directional demixing by means of directional coolingcannot be compared without any objection with directional coagulation bymeans of directional cooling of melts of materials having eutecticcompositions. For directional coagulation there applies that the squareof the lamella distance is inversely proportional to the growth rate, ata constant growth rate in accordance with A v=CD wherein k=lamelladistance v=growth rate C=a constant of the system concerned D=diifusionconstant The following relationship was determined for eutectoidcompositions in case of directional demixing:

This proves that the methods used for directional coagulation cannot beused without difliculty when directionally demixing solid single-phasematerial having a eutectoid composition or of solid solutions. However,if one starts from grains having a diameter of at least 0.1 mm., thetemperature gradient being equal to or larger than 10 C. per cm. and thegrowth by which the temperature gradient is moved through the body issmaller than or equal to the maximum rate of the transformation front,it is found that structures are obtained which are comparable with thestructures obtained when directionally coagulating melts having aeutectic composition. The lamella distance obtained by the methodaccording to the invention is, however, found to be considerably smallerthan the lamella distance which is usualy found at corresponding growthrates when directionally coagulating eutectic melts.

The maximum rate of the transformation front is different for eachsystem, but may be experimentally determined in a simple manner. It wasfound in practice that the maximum rate of the transformation front isgreater as the eutectoid temperature or the saturation temperature ishigher. Usually the maximum rate lies between 10 and l0 -T cm. per hourwherein T is the eutectoid temperature in K. or the saturationtemperature in K. Failure of the experiments which have become known inliterature up till now is probably to be ascribed to the fact that oneor more of the three mentioned criteria are not satisfied. Nodirectional effect was found when, for example, the method Was used onthe systems: 28 at. percent Zn, remainder Fe (solid solution), grainsize approximately 50 11111.; 25 at. percent Sn, remainder Fe, grainsize between 10 and 30 ,um. and 0.8% by weight of C, remainder Fe (afterdemixing pearlite), grain size approximately 20 ,um. The methodaccording to the invention may be performed by means of a techniquewhich is comparable with the Bridgman technique in which the body ispassed through a temperature gradient or in which the temperaturegradient is moved relative to the body. In practice the temperaturegradients to be used may be obtained with comparatively simple standardapparatus. Usually the external temperature gradient to be used is lessthan 450 C./cm. Generally there applies that the temperature gradient ischosen to be so much greater as the grain diameter is smaller. Themethod may be used for reinforcing articles, for example, tools. It isthen possible to subject the articles to mechanical operations, forexample, forging at the temperature above the transformation temperature(eutectoid temperature or the temperature at which saturation occurs) orat room temperature after previous tempering from a temperature abovethe transformation temperature and by subsequently giving the articles agreater strength by means of directional demixing. The method mayalternatively be used to give articles certain magnetical, electricaland/ or optical properties.

In order that the invention may be readily carried into effect, it willnow be described in detail with reference to the few examples.

EXAMPLE I A quartz tube having a length of 10 cms. and an internaldiameter of 0.4 cm. and an external diameter of 0.54 cm. was filled witha molten alloy of nickel and indium (55.5 at. percent In, remainderNi),melting point approximately 950" C., eutectoid temperature 770 C.The alloy was heated for two hours at 1050 C. and it was subsequentlycoagulated by decreasing the temperature to approximately 850 C. Afterthis treatment the grains had a diameter of between 0.5 and 3 mms. Thealloyfilled tube was subsequently passed through a temperature gradientof 65 C. per cm. at a constant rate of 0.1 cm. per hour (Bridgmantechnique). The lamella distance in the directionally demixed body was0.7 ,um. after finishing the treatment, at a rate of 1 cm. per hour: 0.4,um. and at a rate of 7 cms. per hour: 0.2 ,urn. The lamellae in thegrains were parallel to the temperature gradient. The lamellae consistedalternately of NiIn and Ni In EXAMPLE II The method described in ExampleI was used on an alloy of copper and indium (20.2 at. percent In,remainder copper, melting point approximately 700 C., eutectoidtemperature 574 C.). The alloy was heated for two hours at 850 C. andsubsequently coagulated by decreasing the temperature to 650 C. Thegrains of the alloy had a diameter of between 1 and 10 mms. after 2hours of heating at 650 C. in the quartz tube. The external temperaturegradient Was 65 C. per cm. A lamella distance of .038 pm. was obtainedat a passing rate of 0.16 cm. per hour and a lamella distance of 0.21 m.was obtained at a passing rate of 1.15 cm. per hour. The lamellae in thegrains were parallel to the temperature gradient. The lamellae consistedalternatively of 29 at. percent In, remainder Cu and 11 at. percent In,remainder On. In one specimen which in addition to grains of more than0.1 mm. also contained smaller grains (approximately 50 am.) it wasfound that the lamellae in the smaller grains were not directed parallelto the temperature gradient in contrast with the grains of more than 0.1mm. in which this was the case (temperature gradient approximately 30 C.per cm., passing rate 0.5 cm. per hour).

EXAMPLE III The method described in Example I was used on an alloy ofcopper and aluminium (24 at. percent Al, remainder Cu, melting point1100 C., eutectoid temperature 565 C.) which alloy was present in a tubeof A1 The alloy was passed through a temperature gradient immediatelyafter coagulation. The grain diameter was between 0.5 and 1 mm. Thetemperature gradient was 100150 C. per cm. At a passing rate of 0.2 cm.per hour a lamella distance of 0.25 ,um. was obtained, and

at a passing rate of 0.5 cm. per hour a lamella distance of 0.20 pm.was' obtained. The lamellae consisted'alternately of 19.6 at. percentAl, remainder Cu, and 30.3 at. percent Al, remainder Cu. At a passingrate of 0.2 cm. per hour and a temperature gradient of 50 C. per cm. arod was obtained which in the direction parallel to the temperaturegradient had a tensile strength of 113 kg. per sq. mm. The maximumtensile strength of nondirectionally cooled copper-aluminium (24 at.percent Al, remainder Cu) is approximately 68 kg. per sq. mm., inaccordance with recent literature.

EXAMPLE IV The method described in Example I was used on an alloy ofcobalt and silicon (25 at. percent Si, remainder Co, peritecticdecomposition temperature 1219 C., eutectoid temperature 1170 C.). Thetemperature gradient was 300 C. per cm. At a rate of 0.05 cm. per hourthe lamella distance was 1.4 ,um., at a rate of 6 cm. per hour thelamella distance was 0.4 ,urn. The lamellae were parallel to thetemperature gradient. The grain diameter was between 0.5 and 3 mms.

EMMPLE V The method according to Example I was used on a solid solutionof tin in lead (16.6 at. percent Sn, remainder Pb). This solid solutionis oversaturated at temperatures below 148 C. The grain diameter wasbetween 0.5 and 1 mm., the temperature gradient was 100 C. per cm. At arate of 0.05 cm. per hour a lamellar struc ture was obtained having alamella distance of 0.9 pm, the lamellae were parallel to thetemperature gradient.

What is claimed is:

1. A method of producing a composite'of parallel oriented lamella shapedgrains of two different metal phases, said method comprising, heating analloy capable of separating discontinuously into at least two phasesupon cooling, to a temperature above the melting point of the alloy,cooling said melted alloy to a temperature between the melting point ofthe alloy and the eutectoid temperature of the alloy to therebycoagulate the molten alloy and form grains having minimum diameters of0.1 mm. and then further cooling the resultant metal grains to roomtemperature by unidirectionally decreasing the temperature of saidgrains at a rate of at least 10 C. per cm. and not greater than themaximum rate at which the separation of said alloy into two or morephases occurs.

2. The method of claim 1 wherein the rate at which the metal grains areunidirectionally cooled to room' temperature is not greater than 10 -Tcm. per hour wherein T is the eutectoid or saturation temperature inReferences Cited UNITED STATES PATENTS 3,124,452 3/1964 Kraft 75-1353,226,225 12/1965 Weiss 75134 T 3,434,892 3/1969 Heimke 75--135 X3,533,863 10/1970 Lee 75-173 C X 3,542,541 11/1970 Lemkey 75135 X D.DEWAYNE RUTLEDGE III, Primary Examiner J. E. LEGRU, Assistant ExaminerUS. Cl. X.R.

